The ability to apply an area (oval or rectangle) to any command would be both flexible and reliable. Here are some examples of how different actions would behave:
- For movement, units would move to the area, spreading themselves out evenly and stopping.
- For patrol, units would patrol the area in such a way as to cover all of the ground with their line of sight, or radar range in the case of radar units. Offensive units would patrol the area and immediately target and engage any units entering the area based on radar or visual information. This differs from simply drawing automatic patrol routes in the area in that the offensive units are effectively killing anything that enters the area on sight, rather than waiting for the enemies to get close enough to their generated patrol routes.
- For attack, offensive units would bombard the area uniformly with their guns, spread out according to the blast radius of their projectiles.
- For building mass extractors, engineers would put mass extractors on all the mass spots in the area.
- For building all other structures, engineers would build the buildings in a grid, with a density that can be specified while holding the area command modifier key and rolling the mousewheel. A preview of where the structures would be built would be shown, and the command would be executed once the player lets go of the mouse button.
Those are a few examples, but basically for any command, the unit would do the most reasonable thing in the specified area that corresponds with the action chosen, the properties of the unit itself, and the properties of the building being constructed, if applicable.
For engineers, there is also the potential to have different types of area command such as "repair", "reclaim" and "assist", so you can ensure only a specific action will be carried out in the area.
Examples from Zero-K
In Zero-K, area commands are issued by selecting a command, then clicking and dragging a circle from the center outwards. Possible area commands in this game are "reclaim", "repair", "resurrect", "attack", "load", "unload", and "build metal extractors".
When issuing area mass extractor commands to a group engineers, no optimization is done to split the group between mass spots to get the job done faster.